Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $68.35   7.822%   $73.6963   $73.70   $73.70   $73.70  
  Purchase #2 $213.38   3.412%   $220.6605   $220.66   $220.65   $220.70  
  Purchase #3 $247.91   9.717%   $271.9994   $272.00   $272.00   $272.00  
  Purchase #4 $17.52   12.273%   $19.6702   $19.67   $19.65   $19.70  
  Purchase #5 $85.86   9.298%   $93.8433   $93.84   $93.85   $93.80  
  Purchase #6 $84.36   4.814%   $88.4211   $88.42   $88.40   $88.40  
  Purchase #7 $175.42   6.527%   $186.8697   $186.87   $186.85   $186.90  
  7 purchase totals = $892.80       $955.1605   $955.16   $955.10   $955.20